Certain motors, such as those used to power car seat cooling fans, are designed to rotate in both clockwise and counter-clockwise directions. The direction in which such a motor is rotating at any given time is controlled by an input pin on the motor integrated circuit (IC), sometimes known as the SET pin. Typically, applying a SET pin voltage that is below a particular threshold causes the motor to spin in one direction, and applying another SET pin voltage that is above that threshold causes the motor to spin in the other direction.
The SET pin of the motor IC is often coupled to a voltage divider circuit that provides an appropriate voltage to the SET pin. The voltage divider circuit contains one or more resistors, sometimes called “bleeder resistors.” One or both of these resistors can become defective or become detached from the voltage divider circuit—for example, due to excessive jostling or external vibration. When this occurs, the motor—which is rotating in one direction—may immediately begin to rotate in the opposite direction. This abrupt change in rotational direction draws a significant current through the motor IC, thus damaging the motor IC.